Wire arc additive manufacturing (WAAM) attracts much attention due to its unique feature of rapid near net shape forming without die. It has the potential to become an advanced manufacturing technology that can break the bottleneck of alloy development and industrial application for aluminum materials. Wire arc additive manufacturing technology originates from traditional arc welding, and both of them use high-energy arc as heat source and metal wires as raw material. The WAAM technology and equipment development, the solidification and solid state phase transformation performance, microstructures, metallurgical defects as well as mechanical property of aluminum alloys were reviewed. The technique prospects of hot wire and multi-wire additive manufacturing, the unique fabrication manner and the exclusive phase transformation microstructure were discussed. The WAAM-specialized approaches to address the issues of poor manufacturing accuracy, serious porosity and cracking, and unsatisfied mechanical property, including fabrication system development, metallurgical defect controlling, alloy composition and microstructure design and heat treatment optimization were proposed. Such proposals are expected to facilitate the rapid development of high-end, customized and distinguished aluminum alloys via WAAM.
In recent years, the sudden rise of high entropy alloys (HEAs) has become a hot research topic in the field of metal materials. The high entropy alloy is located in the central region of phase diagram, which has broad alloy composition space and possible formation of microstructure. The synergistic regulation of composition and preparation process can obtain richer structure. Unconventional chemical structure is expected to break through the performance limit of traditional anti-wear and lubricating alloys. In this work, the classification of wear-resistant HEAs was discussed. The effects of the addition of chemically active metals, soft metals and refractory metals on the wear resistance and lubrication properties of HEAs were analyzed. The effects of non-metallic elements and ceramic phases on the tribological properties of HEAs matrix composites were summarized. The effects of heat treatment and surface engineering technology on the surface microstructure and tribological behavior of HEAs were reviewed. The design method of HEAs with anti-wear lubrication under severe working conditions was discussed. The future research and application of HEAs in the field of friction and wear were prospected. High entropy alloys have great potential to solve the bottleneck problems of traditional alloys, such as to realize stable lubrication and anti-wear under extreme working conditions and to ensure anti-wear under specific functions.
With the rapid development of portable and wearable electronic devices, research on flexible energy storage devices has gradually shifted to the directions of miniaturization, softness and intelligence. At the same time, people have higher requirements for the energy density, power density and mechanical properties of the device. As the core part of flexible energy storage devices, electrode material is the key to determining device performance. With the development of flexible energy storage electronic devices, there is an urgent need for new battery technology and fast, low cost and precise control of their microstructure preparation methods. Therefore, the research and development of new energy storage devices such as flexible lithium/sodium-ion batteries, flexible lithium-sulfur batteries, and flexible zinc-air batteries have become the current research hotspots in academia. The current research status of flexible energy storage battery electrodes in recent years was discussed in this paper, the design of flexible electrode materials (independent flexible electrodes and flexible substrate electrodes), and the preparation process of flexible electrode materials of different dimensions (one-dimensional materials, two-dimensional materials and three-dimensional materials) and applications of flexible energy storage electrodes (flexible lithium/sodium ion batteries, flexible lithium-sulfur batteries, flexible zinc-air batteries) were compared and analyzed, and the structural characteristics and electrochemical properties of electrode materials were discussed. Finally, the current problems faced by flexible energy storage devices were pointed out, and the future focus of flexible energy storage devices was the research and development of new solid electrolytes, the rational design of device structures and the continuous optimization of packaging technology.
The meaning and characteristics of refractory high entropy alloys were briefly described, and the preparation methods of various refractory high entropy alloys (bulk, film and coating) were summarized.The comprehensive properties of refractory high entropy alloys were emphatically expounded. It was suggested that the composition design should be optimized by constructing a special database of refractory high entropy alloys, and the manufacturability of different preparation methods should be focused on. In view of the shortcomings of high room temperature brittleness, high density and high cost of refractory high entropy alloys at present, different preparation methods could be selected according to the properties of refractory high entropy alloys for future industrial application.
The friction and wear of mechanical parts mainly occurs on the surface of the material, and about 80% of the failures of parts are caused by surface wear.Friction and wear increase the loss of material and energy, and reduce the reliability and safety.Using laser cladding technology to prepare a high entropy alloy coating on the surface of the substrate can achieve a good metallurgical combination between the coating and the substrate, so as to achieve the purpose of improving surface wear resistance.The main factors affecting the wear resistance of the high entropy alloy coating are the mechanical and physical properties of the coating material (such as hardness, plasticity and toughness), defects generated during the cladding process (such as surface roughness, pores and cracks), friction conditions (such as high temperature environment and corrosive environment).In this paper, the influencing factors and strengthening mechanism of laser cladding high entropy alloy coatings were reviewed and summarized.First of all, the influence of laser process parameters (such as laser power, laser scanning speed, spot diameter) and post-treatment processes (such as heat treatment and rolling) on the quality and performance of the coating were explained.Secondly, the influence of component element selection, high temperature environment and corrosive environment on the wear resistance of the coating was described.Finally, the problems existing in the preparation of high entropy alloy coatings by laser cladding technology were analyzed, and the future development trends were forecasted, such as developing new materials based on far-equilibrium material design theory, using electric field-magnetic field synergy or laser-ultrasonic vibration composite technology to improve the wear resistance of coatings, etc.
Ceramics are widely used as dental restorative materials because of their superior wear resistance, chemical stability, biocompatibility, and aesthetic features. In this paper, the chemical compositions, microstructures and mechanical properties of dental ceramics were introduced, based on the wear mechanisms of typical dental ceramics and their abrasiveness with opposing human teeth, the main progress concerning the tribological performance optimization of dental ceramics were summarized, and it was pointed out that the mismatch of tribological properties between ceramics and human teeth seriously restricts the clinical application of dental ceramics. Then the in vitro test methods of tribological properties of dental ceramic materials are analyzed and summarized from the aspects of laboratory test medium, friction pair, load, displacement and cycle times. Finally, the future development trends of dental ceramics were discussed from the perspective of bionic tribology. It was pointed out that bionic design of ceramic matrix composites is a promising strategy for overcoming the mismatch of tribological property between dental ceramic restorations and human teeth.
The formation mechanisms of the precursor film (PF) at high temperature were reviewed, i.e., surface diffusion mechanism, evaporation-condensation mechanism, subcutaneous infiltration mechanism, and rapid absorption then film overflow mechanism. In the experimental metallic systems, the most possible mechanism is the subcutaneous infiltration mechanism, which is related to the apparent contact angle, contact radius, height of gap between the substrate metal and oxide film. In the metal/ceramic system, the formation of precursor film is usually rapid absorption then film overflow mechanism. The appearance of PF for adsorption mechanism needs to meet the contradiction of relative inertia and high affinity at the liquid/solid interface. Meanwhile, another possible mechanism of precursor film in high temperature reactive wetting system, namely film transport mechanism, is introduced. It was pointed out that the difficulty of studying precursor film lies in the unpredictability and instability of precursor film, and its development direction should be systematic, and the corresponding theoretical model should be established.
Natural enzymes are trace proteins produced by living cells in human body. It is precisely because of the existence of enzyme that the daily operation of organisms can be carried out orderly. At present, enzymes are used in many fields such as biomedicine, catalysis and detection. However, natural enzymes have many disadvantages, such as easy inactivation, poor stability, difficult synthesis, complex purification and high price, which hinder the large-scale application. In the past decades, as a new generation of artificial enzymes, nanomaterials mimic enzymes has gradually become a substitute for natural enzyme due to their high stability and good repeatability. Nanomaterial mimetic enzymes play an important role in many fields. The application of nanomaterial mimetic enzymes in the detection of O2·- and salvianolic acid in the field of electrochemical sensing was focused on in this paper, as well as in the detection of small biological molecules such as glutathione, glucose, cholesterol and H2O2, which can effectively detect the content of heavy metal salts and pesticides in the field of environmental pollution prevention and control, nanomaterials mimic enzymes can also prevent cancer, virus infection and other diseases by detecting specific sequences of DNA. Finally, it was expected that the future research of nanomaterials mimic enzymes will focus on the coupling between nanomaterials mimic enzymes, reaction mechanism, optimization of enzyme reaction environment and substrate selectivity, which will be the key research direction in the future.
Polymer materials are widely used in the mechanical lubricant field owing to their light, low-cost, anti-corrosion, and excellent self-lubricating performance. Adding functional fillers with anti-friction and reinforcing character can overcome the inherent defects of intrinsic polymer materials and then obtaining tribological composites materials with the low friction coefficient, high-wearing, high-bearing, and heat-resisting performance. The anti-friction and anti-wear effect and mechanism of composites by adding functional fillers such as carbon-based materials, transition metal sulfides, microcapsules, soft metals, ceramic nanoparticles, mineral salts, and self-lubricant polymer materials were summarized in this paper. Meanwhile, the mechanical property is the key parameter that can guarantee the service performance and application deadline of polymer materials and also gives the significant influence of tribological performance. The enhanced and toughening mechanism of composites by adding nanoparticles and fiber was also mainly discussed in this paper. Finally, The synergistic effect of functional fillers on mechanical and tribological properties was prospected, as well as the development trend of computer simulation in tribology of composite materials.